This invention relates to an improved process for the conversion of phenol to a mixture of hydroquinone and catechol. More particularly this invention relates to a process for the oxidation of phenol to a mixture of hydroquinone and catechol using hydrogen peroxide as the oxidant in the presence of titanium silicate molecular sieves in a multistage fixed bed reactor.
Many processes are known in the prior art for the conversion of phenol to hydroquinone and catechol using hydrogen peroxide, H.sub.2 O.sub.2 as the oxidant. In U.S. Pat. No. 3,929,913, assigned to Brichima, the catalyst used is farrocane, ferrous sulfate chelates are used as catalysts in the U.S. Pat. No. 3,920,756. In the Rhone Poulano process described J. Varagnat in the journal of Industrial Engg. Chemistry, product Research Development, Vol. 15, page 212 (1976), a combination of phosphoric and perchloric acids are used as catalysts. The use of molecular sieves as catalysts for the oxidation of phenol to hydroquinone and catechol using H.sub.2 O.sub.2 as the oxidant is also known. European Patent 0266825 describes the use of crystalline gallium titanium silicates as catalysts. European Patent 0265018 describes the use, as catalysts, of zeolites with a pore diameter between 5 and 12A. Of more relevance to the present invention, U.S. Pat. No. 4,396,783 and U.K. Patent 2116974 both assigned to Enichem claim the use of a titanium silicate molecular sieve, TS-1, in the hydroxylation of aromatics.
In prior art processes using titanium silicate molecular sieves, as for example, the Enichem process, phenol and H.sub.2 O.sub.2 in a molar ratio equal to or lower than 5, are contacted at 60.degree.-150.degree. C. with a titanium cilicate molecular sieve containing titanium in a proportion, calculated as TiO.sub.2, of between 0.1 and 7% by weight and preferably between 2 and 4% wt. to yield the products hydroquinone and catechol. In addition to the above desired products, significant amounts of heavy oxidation products, hereinafter referred to as tar, were also produced in the process. In example 5 of U.S. Pat. No. 4,396,783, for instance, 21% by weight of phenol was converted into by product tar. The tar originates from the further reaction of hydroquinone and catechol at the elevated temperatures during the exothermic oxidation of phenol. Any modification of the process which reduces the formation of tar will constitute a significant improvement of the process.
It is, therefore, an object of this invention to provide an improved process for the oxidation of phenol to hydroquinone and catechol wherein the production of the undesired by product tar is suppressed leading thereby to enhanced yields of hydroquinone and catechol.
Another object of the present invention is to provide a continuous rather than a batch or semibatch process for the oxidation of phenol. Other and additional objects of this invention will become apparent from a consideration of this entire specification including the claims thereof.